When i ejaculate i notice my semen is thicker and clumpier than usual. could an std cause this?

Unlikely: Semen consistency can vary depending on amount of physical activity that day, amount of water consumed, number of times of ejaculation. If concerned, consume plenty of fluids and take a break from ejaculation for a few days. If pain, blood or severe odor develops visit your MD for consideration of STD testing.

Likely: Normal. Usually an indication of long term abstinence. Increasing fluid intake and frequent sex will make your semen lighter